Hi
Am 02.09.25 um 10:30 schrieb Javier Martinez Canillas:
Thomas Zimmermann <tzimmerm...@suse.de> writes:
HyperV's virtual hardware does not provide vblank interrupts. Use a
vblank timer to simulate the interrupt. Rate-limits the display's
update frequency to the display-mode settings. Avoids excessive CPU
overhead with compositors that do not rate-limit their output.
Signed-off-by: Thomas Zimmermann <tzimmerm...@suse.de>
---
Reviewed-by: Javier Martinez Canillas <javi...@redhat.com>
[...]
@@ -111,11 +113,15 @@ static void hyperv_crtc_helper_atomic_enable(struct drm_crtc *crtc,
crtc_state->mode.hdisplay,
crtc_state->mode.vdisplay,
plane_state->fb->pitches[0]);
+
+ drm_crtc_vblank_on(crtc);
}
static const struct drm_crtc_helper_funcs hyperv_crtc_helper_funcs = {
.atomic_check = drm_crtc_helper_atomic_check,
+ .atomic_flush = drm_crtc_vblank_atomic_flush,
.atomic_enable = hyperv_crtc_helper_atomic_enable,
+ .atomic_disable = drm_crtc_vblank_atomic_disable,
};
I think your patch is correct due the driver not having an .atomic_disable
callback. But looking at the driver, I see that its .atomic_enable does:
static void hyperv_crtc_helper_atomic_enable(struct drm_crtc *crtc,
struct drm_atomic_state *state)
{
...
hyperv_update_situation(hv->hdev, 1, hv->screen_depth,
crtc_state->mode.hdisplay,
crtc_state->mode.vdisplay,
plane_state->fb->pitches[0]);
}
and this function in turn does:
int hyperv_update_situation(struct hv_device *hdev, u8 active, u32 bpp,
u32 w, u32 h, u32 pitch)
{
...
msg.situ.video_output[0].active = active;
...
}
So I wonder if it should instead have a custom .atomic_disable that calls:
hyperv_update_situation(hv->hdev, 0, hv->screen_depth,
crtc_state->mode.hdisplay,
crtc_state->mode.vdisplay,
plane_state->fb->pitches[0]);
I'm not familiar with hyperv to know whether is a problem or not for the
host to not be notified that the guest display is disabled. But I thought
that should raise this question for the folks familiar with it.
The feedback I got at
https://lore.kernel.org/dri-devel/sn6pr02mb4157f630284939e084486afed4...@sn6pr02mb4157.namprd02.prod.outlook.com/
is that the vblank timer solves the problem of excessive CPU consumption
on hypervdrm. Ans that's also the observation I had with other drivers.
I guess, telling the host about the disabled display would still make sense.
Best regards
Thomas
--
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstrasse 146, 90461 Nuernberg, Germany
GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman
HRB 36809 (AG Nuernberg)
